The present invention relates to an elastically damping device which is employed in an engine mount of a vehicle.
The elastically damping device comprises a first and a second fluid chambers, which are separated by a partition plate from each other and each of which is defined by an elastically deformable wall. These fluid chambers communicate with each other by way of a restricted passage provided in the partition plate while at least one of these chambers is connected to an engine.
When the engine is started, the vibrations of the engine are transmitted to the fluid chamber to deform the fluid chamber. Due to the increment in inner pressure of the fluid chamber caused by the deformation thereof, the fluid flows from one fluid chamber to the other chamber through the restricted passage at high speed. At this time, the fluid receives a large resistance so that vibrations of low frequency and large amplitude such as cranking vibrations occurring at an engine starting time and shake vibrations occurring while the vehicle is running, can be effectively damped.
While the engine is operated, there occur vibrations of high frequency, of which the frequency is not less than that of idling vibrations and the amplitude is smaller than that of the above described cranking vibrations and the shake vibrations. Such vibrations of high frequency and small amplitude must be not damped but isolated.
For that purpose, the conventional device has adopted such a structure that the whole or one portion of the above described partition plate is provided so as to be movable by a predetermined distance so as to lower the increment in inner pressure of the fluid chamber.
However, the amplitude of the idling vibrations is comparatively larger than that of the vibrations of high frequency, which occur while the vehicle is running. Therefore, when the movable distance of the partition plate is made large so as to isolate the idling vibrations, there occurs the problem that the cranking vibrations and the shake vibrations are not sufficiently damped.